Microfluorometric analysis of the responses of neonatal rat pancreatic islet cells in monolayer culture to intracellular microinjection of tracers (e.g. 6-carboxyfluorescein) or metabolites (e.g. glucose-6-P) reveals that : 1) islet cells do communicate, with intercellular transit times of 0.1-0.5 sec; 2) extracellular glucose levels affect the number and distribution of communicating cells; 3) cultivation of islet cells in glucose-deficient media affects their ability to communicate, as well as the predominance of reduction of reoxidation reactions (NAD(P) NAD(P)H)) in response to injection of glucose-6-P. The kinetics of cell communication will be studied in the presence of a variety of primary stimulants of insulin release, as well as potentiators and inhibitors of insulin release. A dual microinjector can be used to inject independently tracers and triggers of insulin release (Ca ions, cyclic AMP, glycolytic intermediates). Clusters used in fluorometry can be marked and retrieved for identification of A, B, D cells by immunofluorescence and electron microscopy. In view of the accumulating evidence for an essential role of glucose metabolism in triggering of insulin secretion in islet cells, the involvement of intermediary metabolism in a sequence of metabolic cationic secretory events, can be explored by injections of glucose-6-P and modifiers to influence NAD(P)H formation or reoxidation. With simultaneous phase microscopy, and microfluorometry, the superimposition of fluorescence on the phase image has allowed the definition of "communicating territories". Their identification of presence of agents affecting islet cell activity (e.g. isobutylmethylxanthine, glibenclamide), and retrieval of the same cluster for electron microscopy will be correlated to ultrastructure (e.g. distribution and size of intercellular gap junctions). Thus, a model system is provided for in situ evaluation of hypotheses of hypotheses concerning islet cell activity and its regulation.